This invention relates to apparatus for producing an output voltage suitable to power an electronic device.
Electronic devices such as laptop computers, cellular phones, digital camcorders and portable music players are typically powered from an external power source such as line current or the electrical systems of automobiles. Alternatively, the electronic devices may be powered from an internal rechargeable battery.
To power an electronic device externally or to recharge an internal battery of the electronic device, the manufacturer provides an external power supply which may be a switching power supply commonly known as an AC adapter that may weigh close to a pound and may be about six inches long, three inches wide and about two inches high.
The external power supply therefore contribute substantially to the weight of the electronic device since a user would need to carry the external power supply with him to permit the charging of the internal battery and/or powering the device from an electrical wall socket. Furthermore, with a wide range of portable electronic devices available in the market with different power requirements, it may be necessary for a user of these different electronic devices to carry more than one AC adapter.
Some manufacturers propose to resolve the problem by introducing a universal power supply which enables selection of a specific voltage, for example within the range of 3V—24V. This alleviates the need to carry several power adapters to power different electronic devices. The selection of the voltage is normally done via a multi-position switch that in turn controls a voltage converter in the universal power supply to generate an output voltage in accordance with the switch setting. This accommodates the different voltage/power requirements for different devices.
However, there is another incompatibility problem which is faced by the user of such electronic devices. Different electronic devices may use different input sockets with different dimensions and thus such an universal power supply may further comprise a number of different interface connectors to match the power supply's output plug to the input sockets of these electronic devices. These different interface connectors come in different shapes and sizes and are offered by many manufacturers, such as the range of “Adaptaplugs” offered by Radioshack Corporation of Fort Worth, Tex., USA.
To use such a universal power supply, the user selects the required voltage rating and attaches an appropriate interface connector to the output plug of the power supply and then connects the power supply to the electronic device via the interface connector. Thus, the proper use of the universal power supply depends on user's proper selection of the correct voltage requirement in addition to choosing the correct interface connector. The possibility of the user incorrectly or accidentally selecting a voltage unsuitable for a corresponding electronic device's voltage requirement is real and this often results in damage to the device's internal electrical circuitry. There is also a possibility of the user mis-matching the polarity of the interface connector which may also result in electrical damage to the electronic device.
To reduce the chances of damaging the electronic device, some manufacturers incorporate resistor circuitry in the interface connector, for example the range of connectors called “PowerTips” from Targus Inc. of Anaheim, Calif., USA, in which the patentee of the present application understands to be licensed from Comarco Wireless Technologies (patent no. U.S. Pat. No. 6,091,611). The resistor circuitry built into the connector replaces the manual selection of the desired voltage since the resistor circuitry controls the voltage/current supplied to the electronic device. As such, a plurality of interface connectors unique in their physical dimension and resistor circuitry to provide a pre-determined voltage is available which corresponds to the different input socket dimensions and voltage requirements of different electronic devices. This obviates the need for a power converter and a multi-position switch within the universal power supply.
Although such a voltage selection means greatly reduces the possibility of the user selecting an incorrect voltage, it necessitates the manufacturer producing a vast number of interface connectors to accommodate different types of electronic devices. Suppose, for example, that ten different types of interface connectors are required to fit the input sockets of fifty different laptop computers. Suppose further that the input voltages required by these fifty laptop computers are different, say 12V, 15V and 18V. This means that the manufacture needs to have a corresponding number of resistive circuits in the connector to regulate the output voltages. Consequently, the permutations of connectors required to support each of these fifty laptop computers would be thirty. This possibly raises production costs which may ultimately be borne by the end user of such power supplies.
It is an object of the present invention to provide an apparatus for producing an output voltage which alleviates the disadvantage of the prior art and/or to provide the public with a useful choice.